Cannot seem to attach MCP server to claude desktop

[JoshFriedmanO3]

First off, this is so exciting and I cant wait to see where the project goes.

Now, i've been trying to get the typescript "First MCP server" example working within claude desktop. I cannot seem to avoid getting this error: "Could not attach to MCP server weather"

I've ran through the steps entirely, so I think there might be something happening locally that doesn't allow for claude to connect to the server.

Any thoughts?

[jspahrsummers]

If you take a look at the logs, what do those say?

[JoshFriedmanO3]

@jspahrsummers Thanks for the reply, probably should've included those from the start haha.

==> /Users/jfriedman/Library/Logs/Claude/mcp-server-mcp-example.log <==
(node:7615) ExperimentalWarning: The ESM module loader is experimental.
file:///Users/jfriedman/Sites/mcp-test/mcp-example/build/index.js:106
            const title = String(request.params.arguments?.title);
                                                          ^

SyntaxError: Unexpected token '.'
    at Loader.moduleStrategy (internal/modules/esm/translators.js:122:18)
    at async link (internal/modules/esm/module_job.js:42:21)

==> /Users/jfriedman/Library/Logs/Claude/mcp-server-wardrobe.log <==
internal/modules/cjs/loader.js:968
  throw err;
  ^

Error: Cannot find module '/build/index.js'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:965:15)
    at Function.Module._load (internal/modules/cjs/loader.js:841:27)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:71:12)
    at internal/main/run_main_module.js:17:47 {
  code: 'MODULE_NOT_FOUND',
  requireStack: []
}

==> /Users/jfriedman/Library/Logs/Claude/mcp-server-weather-server.log <==
(node:30458) ExperimentalWarning: The ESM module loader is experimental.
file:///Users/jfriedman/Sites/mcp-test/mcp-example/weather-server/build/index.js:93
                    throw new McpError(ErrorCode.InternalError, `Weather API error: ${error.response?.data.message ?? error.message}`);
                                                                                                     ^

SyntaxError: Unexpected token '.'
    at Loader.moduleStrategy (internal/modules/esm/translators.js:122:18)
    at async link (internal/modules/esm/module_job.js:42:21)

==> /Users/jfriedman/Library/Logs/Claude/mcp-server-weather.log <==
(node:33058) ExperimentalWarning: The ESM module loader is experimental.
file:///Users/jfriedman/Sites/mcp-test/mcp-example/weather-server/build/index.js:93
                    throw new McpError(ErrorCode.InternalError, `Weather API error: ${error.response?.data.message ?? error.message}`);
                                                                                                     ^

SyntaxError: Unexpected token '.'
    at Loader.moduleStrategy (internal/modules/esm/translators.js:122:18)
    at async link (internal/modules/esm/module_job.js:42:21)

==> /Users/jfriedman/Library/Logs/Claude/mcp.log <==
2024-11-25T21:33:47.678Z [info] Connected to MCP server weather!
2024-11-25T21:37:01.589Z [info] Attempting to connect to MCP server weather...
2024-11-25T21:37:01.597Z [info] Connected to MCP server weather!
2024-11-25T21:37:01.765Z [error] Error in MCP connection to server weather: SyntaxError: Unexpected token 'W', "Weather MC"... is not valid JSON
    at JSON.parse (<anonymous>)
    at Vwe (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:52:189)
    at qwe.readMessage (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:52:115)
    at Gwe.processReadBuffer (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:53:1729)
    at Socket.<anonymous> (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:53:1520)
    at Socket.emit (node:events:519:28)
    at addChunk (node:internal/streams/readable:559:12)
    at readableAddChunkPushByteMode (node:internal/streams/readable:510:3)
    at Readable.push (node:internal/streams/readable:390:5)
    at Pipe.onStreamRead (node:internal/stream_base_commons:191:23)
2024-11-25T21:37:51.819Z [info] Attempting to connect to MCP server weather...
2024-11-25T21:37:51.827Z [info] Connected to MCP server weather!
2024-11-25T21:45:14.916Z [info] Attempting to connect to MCP server weather...
2024-11-25T21:45:15.013Z [info] Connected to MCP server weather!
2024-11-25T21:46:17.414Z [info] Attempting to connect to MCP server weather...
2024-11-25T21:46:17.421Z [info] Connected to MCP server weather!

I tried directly pointing to the build.js file, but same result. Additionally, my node version is v20.11.1.

I can see the server work within inspector.

the lines:

Attempting to connect to MCP server weather...
Connected to MCP server weather!

have continued after the log above, so maybe something is causing the server connection to drop.

[JoshFriedmanO3]

yeah that was another thought on my end:

[user-path]/.nvm/versions/node/v20.11.1/bin/node
/opt/homebrew/bin/node
[user-path]/.nvm/versions/node/v20.11.1/bin/node

[jspahrsummers]

Well, this probably isn't the whole issue, but I just realized part of our TypeScript "first server" guide is wrong. 😅

Change the console.log to console.error to fix one of the errors here. Servers shouldn't log on stdout, or it can interfere with the protocol communication itself.

I'll get the docs updated!

[JoshFriedmanO3]

happy to help! We'll figure it out!

[rictic]

As an aside, a trick we ran into in wireit, you can replace the global console with one that always writes to stderr, or to any other stream:

globalThis.console = new require('console').Console({stdout: process.stderr, stderr: process.stderr});

[jspahrsummers]

Sorry, I should have realized—this is actually the same issue as modelcontextprotocol/servers#64. Will track it over there, but in the meantime, hopefully the workarounds in that thread help! 🤞

[farkindasales]

{
"mcpServers": {
"filesystem": {
"command": "npx",
"args": [
"-y",
"@modelcontextprotocol/server-filesystem",
"/Users/pc/Desktop/claude"
]
}
}
}

Friends, I am using Win 10. But with this code, Claude gives this error. Is it necessary to install any other add-ons for Windows?

can you help me

[rictic]

If you open a new terminal and run npx -y @modelcontextprotocol/server-filesystem /Users/pc/Desktop/claude does it work? You might need to install NodeJS (which includes npm, npx).

If that does work, try running Get-Command npx (powershell) to get the full path to your npx command. If you replace the npx with the full path to the binary that may help.

[jspahrsummers]

See modelcontextprotocol/servers#40 for this issue.

[TimHuey]

I'm getting the same error. The server spins up, the terminal window shows the message that Brave-Search MCP server is running on stdio and then I get the popup dialog message that is shown above in the claude desktop. Windows 11.

Since it was saying it can't connect I turned off windows firewall and that didn't fix it. I tried switching to the Node version that I have it working with on my mac-mini 20.11.1 and that didn't fix it either. I can spin it up manually by just typing the command line npx command. But that doesn't help it. The npx versions are the same on the mac-mini and the windows computers. I just can't figure out why this isn't working on the windows system.

[jspahrsummers]

Are you running into modelcontextprotocol/servers#40? Do any of the workarounds in that thread help?